1. Field of the Invention
This invention relates to digital color video signal encoders used in color video cameras, and more particularly, to a digital color video signal encoder which reduces the influence of quantum noise on the luminance and chrominance signal components.
2. Description of the Prior Art
A digital color video camera has been proposed which generates digital output signals comprised of eight-bit digital words. An eight-bit digital word can, of course, assume any one of two hundred fifty-six values. Thus, the eight-bit composite video signal from a digital video camera can be said to have a dynamic range of two hundred fifty-six graduations or steps.
However, the full dynamic range of the eight-bit words is not utilized in prior art digital video cameras. Rather, the composite video signals have an upper limit or white level with a selected digital value of "200", and a lower limit or pedestal or black level having a digital value of "60". Thus, the composite digital video signal has a dynamic range of 140 steps or graduations.
The composite video signal from the digital video camera includes a synchronizing signal having a level reduced by a digital value of "56" from the pedestal or black level of "60". Accordingly, the digital value of the composite video signal is "4" for the synchronizing signal. The lower limit of the composite video signal thus has a tolerance or limiting range of "4". The lower limit of the signal in the video region has a digital value of "60" because of the presence of the synchronizing signal. The upper limit of the composite video signal also has to have a tolerance or limiting range. Therefore, the 100% white level of the composite video signal usually has a digital value of "200", rather than the maximum digital value of "255". Thus, the dynamic range of the signal carrying the video information has 200 minus 60, or 140, graduations or steps.
According to one prior art video camera, the dynamic ranges of the luminance signal Y and the chrominance signals I and Q, each being a component signal for the composite signal generated by the video camera, have been compressed to 140 graduations or steps prior to being combined to form the composite signal. However, the component signals Y, I and Q do not include synchronizing signals, which must be added later to the composite signal. Thus, it is desirable to utilize the full range available in an eight bit digital signal in order to reduce quantum noise and its undesirable effects on the composite video signal.